This invention relates to apparatus for forming holes in the upright flanges of elongated structural members such as I-beams, channels and angle irons of the type having a web joined to and projecting horizontally from the flange or flanges, the web actually being a horizontal flange in the case of an angle iron. More particularly, the invention relates to apparatus in which the holes are formed by upper and/or lower punch presses which are mounted on a vertically movable carriage. The upper press is used to punch holes in the upper flange of the I-beam and in the upwardly projecting flange of the angle iron while the lower press is used to punch holes in the lower flange of the I-beam and in the depending flange of the channel.
In the case of an I-beam, the particular vertical location of the holes in the flanges is conventionally spelled out in terms of gage line dimension with respect to a horizontal reference plane which bisects the web. According to conventional standards, the gage line dimension for an I-beam does not represent the actual spacing of a hole from the reference plane but instead is a dimensional number which is equal to twice the actual spacing of the hole from the reference plane. For an angle iron, the reference plane is defined by the lower surface of the horizontal flange while the gage line dimension represents the actual spacing of the hole above the reference plane. The reference plane of a channel coincides with the upper surface of the web and, in the case of a channel, the gage line dimension specifies the actual distance of the hole below the reference plane. Accordingly, the reference planes for the three different types of structural members lie in different locations with respect to the web or horizontal flange and, when dealing with an I-beam, the specified gage line dimension for a given hole is not the actual distance of the hole from the reference plane.
When a structural member is first advanced into position for punching, the reference plane most usually is located at an unknown elevation relative to the presses. Accordingly, it is necessary first to determine the location of the reference plane relative to the presses and then to position the presses in a proper vertical location with respect to the reference plane in order to effect punching of a hole at a specified gage line dimension. Determination of the location of the reference plane of an I-beam is particularly difficult since such plane bisects the web and thus any measurement gaged from a surface of the web must take one-half the vertical thickness of the web into account before the location of the reference plane can be ascertained. Also, the vertical thickness of the horizontal flange of an angle iron must be taken into account when finding the reference plane of the angle iron by measuring from the upper surface of the horizontal flange. In addition, the elevation of the reference plane may vary along the length of the structural member if the member is bowed in a vertical direction.